So, which one of these four shrimps do you think is the best for a 20gal planted aquarium which contains 2 Guppies/1 Dwarf Gourami/2 Cory Cats/3 Neon Tetras (small)?
If you want cheap, go with ghost shrimp. The are 0.15 each at my LFS.
I would go with the Fire or Amano. My LFS sells the Amano's and says they are great algae eaters. The Fire seems about the same but the color would be a great addition to the tank.
As far as the Singapore Flower, a 3.5 inch omnivorous shrimp is boardering on being a crawfish. At that size I would worry about it eating my smaller fish as they slept at night.
I have seen some of mine carrying eggs but I have never seen little ones, but then again, all the fish would probably feast on them the minute they hatch.
My ghost shrimp avoid all of the fish I have which include small fish such as neons, cardinals, and rummies.